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1School of Health and Human Performance,3CLARITY: The Centre for SensorWeb Technologies, Dublin City University, Dublin, Ireland;2Department ofComputer Science, Trinity College, Dublin, IrelandThe purpose of this study was to identify the performance determining factors of the 5-iron golf swing. Joint kinematics were obtained from thirty male golfers using a twelvecamera motion analysis system. Participants were divided into two groups, based ontheir ball launch speed (high vs. low). Those in the high ball speed group were deemedto be the more skillful group. Statistical analysis was used to identify the variables whichdiffered significantly between the two groups, and could therefore be classified as theperformance determining factors. The following factors were important to performancesuccess: (i) the ability of the golfer to maintain a large X Factor angle and generate largeX Factor angular velocity throughout the downswing, (ii) maintain the left arm as straightas possible throughout the swing, (iii) utilise greater movement of the hips in the directionof the target and a greater extension of the right hip during the downswing and (iv)greater flexion of both shoulders and less left shoulder internal rotation during thebackswing.KEY WORDS: golf, joint kinematics, 5 iron, ball launch speed.

INTRODUCTION:Golf is played by 10-20% of the adult population in most countries (Thériault and Lachance1998). The full golf swing using the iron clubs to strike the ball is a key element of success ingolf. Therefore in order to help enhance golfing performance it is important to identify the“performance determining factors” of the full golf swing. Comparison of skilled and lesserskilled golfers’ joint kinematics allows for the identification of these performance determiningfactors. Unfortunately, previous research has focused on the driver club despite the fact thateither an equal or even a higher proportion of shots for maximum distance in the game ofgolf are taken with iron clubs. Only two studies (Budney and Bellow 1982, Cheetham et al.2001) appear to have compared the kinematics of the golf swing of skilled and unskilledgolfers using an iron club. There is a need therefore for research that focuses on golfingperformance using the iron clubs. The aim of the present study is to identify the performancedetermining factors of the 5 iron golf swing through analysis of joint kinematics of skilled andlesser skilled golfers.METHOD:Participants: 30 male right handed golfers (34 ± 16 yrs.) were recruited for the study. Ethicalapproval was received from the Ethics Committee at Dublin City University. All participantswere injury free at the time of the test. Participants underwent a familiarisation session in thelaboratory prior to initiation of testing.

Data Collection: Forty one reflective spherical markers were placed on anatomicallandmarks on the body. A 12 camera (250 Hz) VICON motion analysis system (VICON 512M, Oxford Metrics Ltd, UK) was used to record the motion of the participant throughout thegolf swing. The testing session consisted of a prescribed warm up, recording of fifteen golfswings and a participant selected cool down period. The prescribed warm up consisted offive minutes walking on a treadmill (2.5 km.h-1) followed by 3mins of practice swings. Theparticipants were instructed to ‘hit the ball as hard as possible towards the target-line, withthe aim to maximize both distance and accuracy, as if in a competitive situation’. The ballwas hit from a tee on a Pro V swing analyser (Golftek Inc., USA) into a net located threemetres from the swing analyser using their own 5 iron golf club.

Data Analysis: X factor (relative rotation of the shoulders with respect to the hips), shoulder,elbow, wrist, hip and knee angles and angular velocities were calculated using the 'golf'model (Vicon, Oxford Metrics Ltd, UK). The angle and angular velocity of each variable wasobtained at each of the eight key events during the swing (Figure 1). Results for eachparticipant’s top three trials with regard to ball speed were averaged to create arepresentative trial of their best swing.

Variable Group MidBackswingLateBackswingTop ofBackswingEarlyDownswingangle (°) HBS -49.5 ± 17.6 -42.5 ± 15.1 -28.3 ± 20.9LBS -66.9 ± 15.2 -62.9 ± 14.6 -44.4 ± 17.7angular velocity HBS 198.0 ± 238.2(°.s-1) LBS 36.3 ± 144.4DISCUSSION:Cheetham et al. (2001) was the only previous study found to examine the X Factor anglewhen using an iron club. Their study measured the X Factor at our fourth swing event, thetop of the backswing. Similar to the present study they found no significant differencebetween their highly skilled and less skilled golfers. This finding for the 5 iron differs to recentresearch on the driver which has found significant differences for the X Factor at the top ofthe backswing between golfers of varying skill level (Myers et al. 2008, Zheng et al. 2008). Inthe present study the HBS group had a significantly greater X Factor angle at the events ofearly downswing (ED), mid downswing (MD) and ball contact (BC) (Table 1). They alsoexhibited a significantly greater X Factor angular velocity at mid downswing and ball contact(Table 1). These results suggest that the X Factor angle at the top of the backswing may notbe the most important phase for the X Factor angle. It may be the ability of the golfer tomaintain a larger X Factor angle and generate greater X Factor angular velocity throughoutthe downswing that contributes to producing higher ball speeds. No previous studies usingan iron club have examined this. The HBS group kept their left elbow more extended thanthe LBS group at four consecutive events (from mid backswing to early downswing) (Table2). The postulated benefit of this is the more extended a golfer keeps their arms the greaterthe velocity the club head is capable of generating since the club head travels through alonger arc in a given time and therefore moves faster (Broer 1973). The right hip wassignificantly more abducted for the HBS group (Table 3) resulting in them moving their hipsmore in the direction of the target during the downswing than the LBS group. The right hip forthe HBS group was also more extended from mid downswing to mid follow through (Table 4);this is likely to aid in the faster transfer of weight to the front foot. Greater right hipflexion/extension angular velocity was evident for the HBS group at early and mid downswing(Table 4). This ability to generate higher velocities early in the concentric phase (downswing)by the HBS group possibly contributed to their greater club head speed by employing a moreenhanced utilisation of the stretch shortening cycle. The increased velocity of the hips earlyin the downswing also possibly indicates the HBS group’s superior use of proximal to distalsequencing as they reached higher velocity of the proximal segment (hips) early in theconcentric movement which possibly led to their higher velocity at the distal segment (clubhead). Results for left and right shoulder flexion/extension angles (Table 5) showed that theHBS group flexed their shoulders more during the backswing (at events mid backswing, latebackswing and top of backswing), thereby utilising a greater range of motion in thebackswing. This appears to have allowed the HBS group to produce greater extensionangular velocity in both shoulders at early downswing. This is possibly due to effectiveutilisation of both the impulse-momentum relationship and utilisation of the stretch shorteningcycle; with a greater angular velocity of the left shoulder by the HBS group evident at midand late backswing. Higher velocities during the backswing increase eccentric loading, whichincreases the potential for enhancement in the concentric phase (downswing) through thestretch shortening cycle (Cavagna et al. 1968, Bosco et al. 1981), as evident by thesignificantly greater angular velocity during early downswing for the HBS group. The HBSgroup used less left shoulder internal rotation than the LBS group during the backswing(Table 6), despite producing a significantly greater angular velocity during early downswing.The smaller rotation may make use of an enhanced utilisation of the stretch shortening cycle(Moran and Wallace 2007).CONCLUSION:Clear performance determining factors are evident for swinging a 5 iron golf club to hit a ballas far and as accurately as possible. It is likely that maintaining a large X Factor angle andincreasing X Factor angular velocity during the downswing could benefit golfers in increasingtheir ball launch velocity with the 5 iron club. In relation to the arms, greater ball velocity maybe generated by maintaining the left arm as straight as possible throughout the swing, as thiswould increase the arc the club head travels through and therefore increase its velocity. Agreater transfer of weight from the back to the front foot from early downswing through to ballcontact brought about by greater movement of the hips in the direction of the target and agreater extension of the right hip allows greater force generation in the direction of the target,which can be transferred to the club to produce greater ball velocity. A greater flexion of bothshoulders and less left shoulder internal rotation during the backswing in the direction of thetarget could also contribute to greater ball velocity generation.